Vaccination is the administration of antigenic material (a vaccine) to stimulate an individual's immune system to develop adaptive immunity to a pathogen. The aim of this study was to analyze the determinant factor of vaccination status of under five children in South Omo zone, SNNPR, Ethiopia using binary logistic regression model. Thus from 174 children under investigation 47(27%) of children are not fully vaccinated and 127(73%) are fully vaccinated. Woreda, household sex, religion, mother education level, child sex and child order are the most factors that affect the vaccination status of children. Full vaccination status of children is more likely for children from educated mothers as compared to those from illiterate mothers. The odd of female children to be full vaccinated was increased by 51%. First (OR: 0.401, 95% CI: 0.091, 1.763) and third order (OR: 0.219, 95% CI: 0.051, 0.931) children are associated with full vaccination status of children negatively. Second (OR: 1.128, 95% CI: 0.281, 4.526) and fourth birth order (OR: 1.034, 95% CI: 0.233, 4.58) children are more likely to be vaccinated than first and third order children. Children from female household are highly related to be fully vaccinated than children from male household. Children from orthodox (OR: 1.88, 95% CI: 1.177, 3.002) family are more vaccinated than the Muslim, catholic and Protestant.